The present invention relates to electroluminescent devices and particularly electroluminescent devices having a short transient response time.
Electroluminescent devices and specifically light emitting diodes (LED) generate incoherent optical radiation through the recombination of pairs of oppositely charged carriers. In a field, such as optical communications, where light emitting diodes are coupled into light transmission pipes, the transient response time, also known as the rise time, of the LED with respect to the LED's modulated input signal becomes very critical. The transient response time of an LED is the time it takes for the optical radiation output to reach about 90% of its maximum output after the application of a step input current. Ideally the transient response time for an LED used for optical communications should be short, i.e. on the order of a few tenths of a microsecond or less.
In the prior art a typical LED had a P type conductivity region of GaAs contiguous to an N type conductivity region of GaAs with both regions being doped by the amphoteric conductivity modifier silicon. This typical LED of the prior art is described in the article entitled "Electroluminescence Characteristics and Efficiency of GaAs:Si Diodes" by I. Ladany, J. Appl. Phys. Vol. 42, No. 2, February, 1971, pages 654 to 656. While this typical prior art LED had an efficiency of 32%, its transient response time, of approximately 1.5 to 2.0 microseconds for a pulse current input, is not ideally suited for applications requiring a short response time. Generally, achieving a short response time was at the cost of efficiency, i.e. the shorter the response time the less efficiency in converting current to optical radiation. Therefore, it would be most desirable, especially in the optical communications field, to have a high efficiency LED with a short transient response time.